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Build the Interphone: a 10-station exchange for your home; Pt.2 In this final article on the Interphone, we give the assembly details and the installation procedure. Depending one how many remote station boards you build, you can connect up to 10 tone dialling phones to the system. By JEFF MONEGAL The construction of the PC boards for this project requires no special care or attention , just a fine soldering iron tip and some patience. Start by going over the PC boards, looking for problems such as shorted tracks or fine breaks in the copper pattern. Any faults fixed now will save a lot of time later. How many phones do you want to be able to connect? The standard remote station board will accommodate up to three phones so if you make two remote station boards, you can have six phones; if you build three remote station boards you can have nine phones. If you want the full 10 phones that the system is capable of, you will need to build a single station board in addition to three standard remote station boards. When it comes to building the remote station boards, we suggest you build just one standard 3-station board first. That way, if you do find problems, they will have been corrected by the time you come to build the other boards. ERPHClNE A large plastic case accommodates virtually all of the circuitry, including the base station board & the remote station boards. A buzzer & a Busy LED are also installed at each extension & wired to a standard telephone socket. 46 STLICON CHTP We also suggest that you complete each board before starting on the next. Our prototype used IC sockets but these can be regarded as optional. They do provide an advantage if you have to troubleshoot the circuitry later. Let's start with the base station board. The wiring diagram is shown in Fig.3. Make and insert all the wire links first and then install the smaller components such as resistors, diodes and small capacitors. Next, install the electrolytic capacitors and integrated circuits, paying particular attention to the orientation of the ICs which will be damaged if they are incorrectly installed. The same comment applies to the installation of the 3terminal regulator and the transistors. Complete the base station PC board assembly by inserting all the remaining components such as the isolation transformer, 12V relays and the crystal. Our prototype boards also used PC-mount screw terminal blocks which are handy for making all the off-board terminations . Note that three insulated wire links must be installed on the copper side of the board - ie, from A to A, B to B and C to C. With the base station board complete, go over your work carefully, comparing it to the wiring and circuit diagrams. This done, you can turn your attention to the remote station board. The wiring diagram for the 3station board is shown in Fig.4. Don't forget that each remote station unit has to be programmed with an identification number before final installation. Each station should use a different output link option from IC10 so that when any extension is paged from another, only one extension will respond. Remote station 1 (ie, extension 1) should have a link from the cathode of diode DZZ to pin 14 ofICl0. Station 2 should have the Fig.3: make sure that all parts are correctly oriented when building the base station board. Note that three wiring points marked A, B & C must be linked to three similarly marked wiring points using insulated wire on the track side of the board (ie, A-A, B-B & C-C). Fig.4 (right): this is the parts overlay for the remote station board. Each remote board accommodates up to three stations & you can build a maximum of 10 stations. Note that each station must use a different output link from IClO - see Table 1. link from D22 to pin 2 ofIClO. Station 3's link would go to pin 15 of IClO and so on up to a maximum of 10 station units. The full list of remote station links (from IClO) is shown in Table 1. Each remote station board should be labelled to show which extension number it is coded for. This will simplify the installation procedure. Case wiring When all the PC boards are fully assembled, the next stage is to install them in the case and complete all the wiring. Our prototype used a large instrument case which accommodates all the PC boards with space to spare. Our prototype also had the boards Table 1: Remote Station Links Extension IC10 Pin No. 0 Pin 3 1 Pin 14 2 Pin 2 3 Pin 15 4 Pin 1 5 Pin 6 6 7 Pin 7 ! Pin 4 8 Pin 9 9 Pin 5 mounted on a baseplate made of PC board material as can be seen in the photos. However, this was a carryover from an earlier version and is not really necessary; you can mount the boards directly into the case. The base station is mounted by itself on the lefthand side of the case while the remote station boards are stacked on each other, on the righthand side of the case. Our prototype was wired using conventional 4-core telephone cable and with standard Telecom-style phone sockets on the rear of the case. However, the wiring itself is not standard. The wiring of the various pins in the sockets is as shown in Table 2. As you can see, pins 2 and 6 are SEPTEMBER1992 47 ,. This view shows how the boards are mounted inside the case. The base station is on the left, while the remote station boards are stacked on each other to the right. Note that the base station board was modified after this photo was taken. used for the internal line connections and so are compatible with any standard DTMF (tone) phone. You can now complete the wiring inside the case. This includes the wiring to the front panel LEDs, the AC plugpack socket and the incoming phone line plug. System testing The first step is to check the DC supplies generated by the circuit. Connect a 12VAC plugpack and use a multimeter to check the +50V and +5V supplies on both the base station and remote station PC boards. Check for the presence of +5V at the supply pin of each IC and also at the collectors of transistors Q4 and Q5. Check for the presence of +50V at pin 6 of each extension socket and also at the collector of Q7, the buzzer driver on each remote station board. Now put the whole system aside and begin modifying the extension 48 SILICON CHIP handsets you will be using. Each one will require the addition of a buzzer and a red LED (Busy LED). Depending on the type of handsets you are going to use, the buzzer and Busy LED may be installed in the base, the cradle or, if it is a one-piece phone, in the receiver itself. One side of the buzzer and the negative connection (K) of the red Busy LED connect to the GND line (pin 2 of the extension socket). The other side Table 2: Socket Connections Pin 1 No Connection Pin 2 GND Pin 3 Busy LEDs Pin 4 No Connection Pin 5 Buzzer Pin 6 Phone Line I, .. of the buzzer connects to the buzzer line (pin 5 of the extension socket), while the positive side of the Busy LED connects to pin 3 of the socket. When your tone phones are suitably modified, you are ready to connect and test the complete system. Connect at least two extension phones to the system and apply power. Lift the handset and the Busy LEDs should start flashing. Now press the# button. The Line LED should light. Hang up the handset and both the Busy and Line LEDs should go out. Pick up the phone again and press the * button and the Hold LED should light. Now press the# button and the Hold LED should go out again while the Line LED goes back on. Press the * button and the Hold LED should light and stay alight when the phone is hung up. After about 30 seconds, the buzzer will sound, warning you that a call is still on hold. At this stage, you have tested most of the functions of the base station. Now try calling another extension. Pick up a phone and press the wanted The rear panel of the case carries standard telephone sockets for the connections to the extension telephones, plus a power socket for the plugpack supply. The two sockets at lower left are not used in the final version. number of another extension for at least two seconds. The ringer in the wanted extension should then sound for as long as you hold down the number button. If you now pick up the other phone, you can have a 2way conversation on two phones between yourself and yourself - great if you are a split personality! Better still, get a friend to pick up the other phone and talk to him or her instead. You can now connect as many handsets as desired and repeat the tests to make sure that all is well. Finally, you are ready to connect the incoming phone line. The Interphone is connected in parallel with an existing tone phone. Now pick up an extension phone and press the # button. You should now hear a dial tone in the earpiece. Dial a number to confirm that all is correct. To hang up, you simply replace the handset. Pick up the phone again and press the # button. Dial a friend and wait until you hear them talking. Inform them as to what you are doing and that they should not hang up the phone. Press the * button, then wait a few seconds then press the # button again. Your friend should still be on the WARNING! In order to comply with the Telecommunications Act, we dri3-w the reader's attention to the following: "This customer equipment has no AUSTEL permit and mat be dangerous or damage a telecommunications network. Connection to a telecommunications network is an offence under section 253 of the Telecommunications Act 1991 and may attract a maximum fine of $12,000". line and you should be able to talk as normal. Now check that you can transfer you call to another extension phone using the # button and the appropriate number button. If all is well, the Interphone is working as it should. You can now run 4-core wiring and wire phone sockets to each point in your home requiring an extension. Once this has been completed, power the whole system up again and go through the functions again to ensure that all is working properly. Kit availability At the time of writing, the copyright for this project has been sold to Altronics of Perth. They should have kits available shortly after this issue goes on sale. Readers should contact Altronics for details of kit prices. The author and designer of the Interphone project will be offering a repair service for readers who need it. He can be contacted at PO Box 33, Condell Park, NSW 2200. Phone (02) 708 3763. SC SEPTEMBER1992 49